Electric circuit breaker



Oct. 6, 1964 R. B. sHoREs ELECTRIC CIRCUIT BREAKER 3 Sheets-Sheet 1 Filed NOV. 2l, 1962 fau ATTORNEY.

Oct. 6, 1964 R. B. sHoREs ELECTRIC CIRCUIT BREAKER 3 Sheets-Sheet 2 Filed Nov. 2l, 1962 /N VENTOR.' ROA/ALD B. SHQ/ess,

A TTORNEY.

United States Patent O 3,152,283 ELECTRIC CIRCUIT BREAKER Ronald B. Shores, West Chester, Pa., assignor to General Electric Company, a corporation of New York Filed Nov. 21, 1962, Ser. No. 239,206 14 Claims. (Cl. 317-15) This invention relates to an electric circuit breaker of the type that comprises one or more interrupting heads, each head comprising two pairs of separable contacts and a metallic housing at high potential that is electrically connected to one contact of each of the two pairs. An example of .this type of circuit breaker is illustrated in U.S. Patent 2,931,951, Wilson, assigned to the assignee of the present invention, where the metallic housing comprises a tank that surrounds the two pairs of contacts.

There has been an increasing demand for circuit breakers with higher and higher continuous current ratings. One way of meeting this demand is to connect a second circuit breaker in parallel with the lirst circuit breaker so that the total continuous current is shared by the two circuit breakers. This approach can be used with the type of circuit breaker shown in the Wilson patent, but a number of problems arise in following it. One of these problems is that an unduly large number of expensive insulating supports are required for the interrupting heads if two duplicate circuit breakers are to be used. Another problem involved in this approach is that it does not readily lend itself to circuit applications where an odd number of breaks in series might be needed. In this respect, when it is desired to have more than two breaks in series, an additional and identical interrupting head is connected in series with the first head. This additional head also includes two breaks in series, so a total of four breaks are present if identical heads are used. In some cases only .three breaks in series may be needed. So there is one superuous break that cannot readily be eliminated so long as identical heads are used. The presence of this superfluous break is undesirable because it unduly increases the cost of the circuit breaker.

Accordingly, an object of my invention is to provide a circuit breaker that comprises substantially identical heads, each comprising two pairs of separable contacts and a metallic housing connected to one contact of each of the two pairs that can readily be arranged to provide an odd number of breaks in series and an equal number of breaks in parallel to the odd number of breaks in series.

Another object in to construct a circuit breaker with parallel connected breaks in such a manner as to require a relatively small number of insulating supports.

In the circuit breaker of the Wilson patent, there is a current transformer assembly that controls the protective relaying equipment associated with the circuit breaker This current transformer assembly is located at one electrical side of the contacts of the circuit breaker and serves as a support for one of the interrupting heads of the circuit breaker. The special construction of the current transformer enables it .to perform relaying functions that had customarily required two current transformers, one at each side of the circuit breaker.

Another object of the present invention is to construct a circuit breaker that has parallel connected breaks in such a manner that a single current transformer of a design corresponding to that of the Wilson patent can be relied upon for performing the usual relaying functions.

In carrying out the invention in one form, I provide an electric circuit breaker comprising a metallic tank at high potential. insulating means is provided for supporting the tank and electrically isolating it from ground. A rst and a second pair of separable contacts are disposed within the tank, and a pair of spaced apart conductors` "ice u project into the tank for carrying current to and from the contacts. insulating means is provided for insulating the conductors from the tank when the contacts are open. Means is provided for electrically connecting one contact of said pairs to the tank. Means is also provided for electrically connecting the other contact of the first Contact pair to the inner end of a first one of the conductors so that said lirst pair of contacts and said first conductor are connected in series between the tank and the outer end of said first conductor. Means is also provided for electrically connecting the other contact of the second contact pair to the inner end of the second of said conductors so that said second pair of contacts and said second conductor are connected in series between said tank and the outer end of said second conductor. Additional means is provided for electrically connecting the series combination of said first conductor and said first pair of contacts in parallel with the series combination of said second conductor and said second pair of contacts.

For a better understanding of the invention, reference may be had to the following description ltaken in conjunction with the accompanying drawing, wherein:

FIG. 1 is a side elevational view partially in section showing a circuit breaker embodying one form of the present invention.

FIG. 2 is an end view of the circuit breaker of FIG. l.

FIG. 3 is a sectional view taken along the line 3-3 of FIG. l.

FIG. 4 is a sectional view taken along the line 44 of FIG. 2.

FIG. 5 is a schematic illustration of a power system containing the circuit breaker illustrated in FIGS. 1-4.

FIG. 6 shows a modified form of the invention.

Referring now to FIG. l, the circuit breaker A shown therein comprises a metallic tank or housing 12 mounted atop an enclosure 14 partially of insulating material. The tank 12 is at a high voltage with respect to ground, and the insulating enclosure 14 serves `to electrically isolate the tank from ground as well as to support the tank 12. Within the tank or housing 12 are two pairs of separable contacts 16 and 18. The inner contacts of each of these sets of contacts 16 and 18 are electrically connected together by a conductor 19 which, in turn, is electrically connected to the tank 12 by means of a conductor 20 so that the tank is at line potential when the contacts are closed.

The contacts are arranged to be simultaneously operated by means of an operating mechanism schematically illustrated at 22. The tank is filled with pressurized gas that serves both as an arc-extinguishing medium and as a medium for actuating the operating mechanism 22. The contact structure and the operating mechanism correspond to those disclosed in detail and claimed in U.S. Patent 2,783,338, Beatty, assigned to the assignee of the present invention and will be described in the present application only to the extent believed necessary to convey an understanding of the present invention. Reference may be had to the Beatty patent if a more detailed description is desired.

For supporting the outer contact of each pair of contacts, a pair of rigid conductors shown schematically at 26 and 28 projecting through opposite ends of the tank 12 are provided. These conductive studs 26 and 28 are respectively enclosed at their outer ends by porcelain cylinders 30 and 32, whichy serve also to support the studs 26 and 2S. These porcelain cylinders are, in turn, suitably supported on the metallic tank 12 at their inner ends. A porcelain cylinder 30 or 32 and a conductive stud 26 or 23 carried thereby is referred to hereinafter as ak terminal bushing. `The tank 12, the circuit breaker structure located within the tank, and the two terminal bushings constitute an assembly 34 which is referred to hereinafter as an interrupting head.

The tank 12 constitutes one terminal of the interrupting head 34, and the outer ends of the two studs and 2S constitute opposite terminals of the interrupting head. Current may flow between the tank 12 and either of these opposite terminals via a irst path which comprises conductors 2@ and 19, contacts 16 and stud 26 or via a second path which comprises conductors 21B and 19, contacts 1S and the other stud 28. As will soon be explained, the outer ends of the two studs 26 and 23 are electrically connected together and to a power line 11. It can therefore be seen that the contacts 16 are connected in parallel with the contacts 13 between the power line 11 and the tank Ztl.

The insulating enclosure 14 that supports the interrupting head 3ftcomprises a tubular porcelain column provided with suitable fastening structure 36 at its top for rigidly securing the tank 12 to the top of porcelain column 35. At the lower end of the porcelain column a metallic tank 38 is provided. The upper portion of this tank 38 comprises a tubular throat 39, which is shown fastened to an annular plate itl that, in turn, is bonded to the porcelain column 35. Together the porcelain column 35 and the lower tank 3S form an en* closure 14 that is rendered gas tight by suitable seals and gaskets provided at all of its joints. It is to be understood that the space within the enclosure 14 is preferably isolated from the pressurized gas within the tank 12.

The lower tank 38 supports the porcelain column 35, A

which, in turn, supports the interrupting head 34. The tank 38 is solidly connected to ground by a connection t4 provided at a suitable location below the throat 39 of the tank. The porcelain column 35 provides for electrical isolation between the high voltage parts of the circuit breaker and the grounded tank 38.

For controlling protective relays associated with the circuit breaker, a current transformer assembly similar to that illustrated and claimed in the aforementioned Wilson patent 2,931,951 is provided. This current transformer utilizes the enclosure 14 as its own enclosure. This enclosure 14 is filled with an insulating fluid, preferably sulphur hexalluoride, in which the various components of the current transformer are disposed. The primary circuit of the current transformer is of a loopshaped form and comprises a pair of co-axially disposed conductors, or arms, Sil and 51 extending through the porcelain column 35' into the tank 38 where their lower ends are electrically joined by a generally toroidal shaped conducting element 52. More specifically, the conductive arm 5t) comprises a rigid stud extending through the insulating column 35 into the tank 38, and the conductive arm 51 comprises a rigid tube surrounding the other conductive arm 5ft and locally insulated therefrom. The toroidal shaped conductor 52 is provided with a gap 52a to render it non-continuous and has its ends on opposite sides of the gap locally insulated from each other and electrically joined to the lower ends of the conductors 56 and 51, respectively.

The upper end 53 of the tubular conductor 51 may be thought of as the line terminal for the current transformer primary, and the upper end Sd for the stud 5t? may be thought of as the circuit interruptor terminal of the current transformer primary. The line terminal 55 of the current transformer is electrically connected to a power line 11. The power line 11 that is connected to the line terminal 53 is divided into two parallel-connected branches 11a and 11b, as will be apparent from FIG. 3. Referring to FTG. l, branch 11a is connected to the line terminal 53 by means of a tubular conductor 56a, whereas branch 11b is connected to the line terminal 53 by means of a second tubular conductor Seb. The tubular conductor 55a, is electrically connected at its lower end to the line terminal 53 and is supported at its upper end on the insulating cylinder 30, where it is locally insulated from conductive stud 26. The tubular conductor Seb is electrically connected at its lower end to the line terminal 53 and is supported at its upper end on the insulating cylinder 32, where it is locally insulated from the conductive stud 28. The electrical connection between the two tubular conductors 56a and Seb and the line terminal 53 is preferably provided by means of a conductive disk 57 extending across the porcelain column 35 and suitably electrically connected to the tubes 56a and Seb and the line terminal 53. This disk 57 also serves to support physically the primary conductor 51, 52, 50.

The circuit interrupter terminal 54 of the current transformer is connected to the two studs 26 and 28 of the circuit interrupter by means of two conductors 58a and SSI), respectively. Conductor 53a extends from terminal 54 to the stud 26 through the tubular conductor 56a, whereas conductor 58h extends from the terminal 54 to the stud 28 through the tubular conductor Seb. The length of conductor 58a is locally insulated from the tubular conductor 56a surrounding it so that current flowing between these two parts is forced to follow a path through the primary winding 50, 52, S1 of the current transformer inasmuch as the only connection between these parts is through the primary winding. Similarly the length of conductor 5S!) is locally insulated from the tubular conductor 56h and is connected to the tubular conductor Seb only through the primary winding Sti, 52, 51, so that current flowing between the parts 58h and 56h must follow a path through the primary winding of the current transformer. The conductors 58a and 58h present parallel paths for current flowing into the circuit interrupter from the circuit interrupter terminal 54 of the current transformer.

As was pointed out hereinabove, the tank 12 constitutes one terminal of the interrupting head 34. Current flows between this terminal 12 and power line 11 by either one of two parallel connected paths. One path is through the branch 11a, tubular conductor 56a, the current transformer primary d1, 52, Si), conductor 58a, stub 26, contact 16 and conductors 19 and 21B. The other path is through the branch 11b, tubular conductor 5612, the current transformer primary 51, 52, 50, conductor 58h, stud 28, contacts 18, and conductors 19 and Ztl. In effect, the current transformer primary winding 50, 52, 51 is connected 1in series with the parallel combination of the two pairs of contacts 16 and 1S. This can be seen quite clearly in the schematic diagram of FIG. 5.

To render the circuit breaker suitable for higher voltages, a second interrupting head 134 is mounted on the first interrupting head This second interrupting head 13dis identical in construction to the first interrupting head and will therefore not be described in detail. To facilitate an understanding of the second interrupting head, however, corresponding parts of the two heads have been assigned reference numerals which correspond in their last two digits. The metallic tank 112 of the second interrupting head is mounted on the tank 12 of the first interrupting head by means of a metallic tube 169 that serves to conduct current between the two tanks 12 and 112. Current flowing through this tube 100 can follow either one of two alternate paths through the interrupting head 13d. One path is through conductors and 119, contact 116 and stud 126 to the outer end of the stud 125. The other path is through conductors 1249 and 119, contacts 113, and stud 128 to the outer end of stud 12S. lt will therefore be seen that in the second interrupting head, contacts 116 are connected in parallel with contacts 118.

To render the circuit breaker suitable for still higher voltages, a third interrupting head 234, best shown in FIGS. 2 and 4 is provided. This third interrupting head 234 is mounted on an insulating column 114 adjacent the first insulating column 14. This third interrupting head is substantially identical to the first and second interrupting heads and will therefore not be described in detail. However, to facilitate an understanding of the third head, the parts of this third head which correspond to similar parts in the other interrupting heads will be assigned reference numerals that correspond in their last two digits to the reference numerals of the other heads.

Referring now to the third interrupting head, the outer end of the stud 226 is electrically connected to the outer end of the stud 126 of the second head by means of a conductor 200. The outer end of the other stud 223 of the third head is electrically connected to the outer end of stud 128 of the second head by means of a conductor 201. In the third interrupting head, current may flow between the tank 212 and the outer ends of the two studs 226 and 228 via either one or two alternate paths through the interrupting head. One path is through conductors 220 and 219, contacts 216, and stud 226 to the outer end of the stud 226. The other path is through conductors 220 and 219, contacts 218, stud 22S to the outer end of stud 228. It will therefore be seen that in the third interrupting head the contacts 216 are connected in parallel with the contacts 21S. A power line 240 is connected to the tank 212 of the third head to carry current to and from the circuit breaker.

The three operating mechanisms 22, 122, and 222 are pneumatically coupled together (in a known manner) so that they can be simultaneously operated to cause all of the contacts of the circuit breaker to open substantially simultaneously during an opening operation and to close substantially simultaneously during a closing operation.

FIG. 5 is a simplified wiring diagram of the circuit breaker assembly described hereinabove. It will be noted that there are two alternative paths through the circuit breaker assembly, one through the series combination of contacts 16, 116 and 216 and the other through the series combination of contacts 18, 118 and 218. These two paths are effectively in parallel and each contains three sets of contacts in series. Current is divided substantially equally between these two paths because each of the two paths have substantially the same, impedance. In this regard, note that each of the paths is substantially identical in construction. The fact that the two conductors 58a and 58h are coaxially disposed relative to tubular conductors (56a and 56b) carrying substantially equal currents assures that the effective reactance of these conductors 58a and 58h will be substantially the same. The parallel relationship of the two paths and the substantially equal division of current between them enables the circuit breaker to carry on a continuous and momentary basis substantially twice as much current as it could safely carry if only one path was available for the current.

It will be noted that, even though each interrupting head contains two breaks, I have been able to provide an odd number of breaks in series without any superfluous breaks being present. This, it will be recalled, was one of the objects of the present invention. If the breaks of each interrupting head had been connected in series with each other, as in prior constructions, it would have been possible to provide only an even number of breaks in series if identical interrupting heads were utilized.

Referring to FIG. 1within the current transformer enclosure, `secondary windings 60 and 61 corresponding to similarly designated secondary windings in the aforementioned Wilson patent are provided. The present application will include only a brief summary of the operation of these windings, and reference may be had to the Wilson patent for a more complete description of their operation if desired. As in the Wilson patent, secondary winding 60 is connected in a differential' protective circuit 80 (best shown in FIG. L5) that defines a first protective zone in which the power circuit 11 is located. The other secondary winding 61 is connected' in a differential protective circuit 82 that denes a second protective zone that includes most of the circuit breaker assembly A and the power circuit 240 at the other side of the circuit breaker assembly, as is shown in FIG. 5. The flow of current into the power circuit 11 from its remote end is controlled by a circuit breaker B shown in FIG. 5; and the flow of current into the power circuit 240 from its remote end is controlled by a circuit breaker C shown in FIG. 5. Any faults to ground occurring in the first protective zone causes the differential protective circuit Si) to operate a relay '70 that effects opening of the circuit breakers A and B. Any fault to ground occurring in the second protective zone causes the differential protective circuit S2 to operate a relay 71 that eifects opening of the circuit breaker A and C.

Even though there are two parallel paths provided through the circuit breaker assembly, I am able to perform the usual protective relaying operations, described hereinabove, with only a single current transformer assembly at one side of the circuit breaker. In this regard, note that the total current follows only a single path 51, 52, 56 in flowing through the current transformer assembly. This path is split into two branches outside the current transformer assembly but not inside it. Thus, the current transformer secondary windings 60 and 61, which are coupled to the undivided primary circuit, can be connected in conventional differential protective circuits S0 and 82, and no allowance need be made for the division of the primary circuit which is present outside the current transformer assembly. Note also that the auxiliary current transformer 35 is capable of distinguishing between internal and external faults in the same manner as it was in the circuit breaker of the Wilson patent.

To enable the relaying system to distinguish between a fault internal to the circuit breaker A and one external to the circuit breaker, an auxiliary current transformer winding is provided. This auxiliary current transformer winding corresponds in structure and operation to a similarly designated current transformer winding in the aforementioned Wilson patent. This auxiliary current transformer winding encircles both conductors, or arms, 5() and 51 of the current transformer primary winding. As shown in FIG. 1 this auxiliary winding 85 is disposed externally of the enclosure 14 in the region of the throat 39 of the tank 38 and is supported by suitable means 87 projecting outwardly from the throat 39. Preferably, this auxiliary winding 85 is wound about an annular magnetic core 85 encircling both the throat portion 39 of the tank and the two arms 50 and 51 of the primary winding. The turns of the winding 85 are insulated from each other and from the core 86 and the support S7 in a conventional manner.

The coil of a relay 9b is connected across the terminals of this winding 85 so that the relay coil can be energized from the winding 85. When a net current exceeding a predetermined amount flows through the region encompassed by the magnetic circuit, or core, 86, sufficient current is induced in the current transformer winding 85 to effect operation of the relay 90. Operation of the relay 90 closes a set of contacts 92 to complete a suitable trip circuit for the breakers A, B, and C.

So long as the primary circuit 5t), 51, 52 of the current transformer assembly is sound, the winding 85 will not be eifemtively energized inasmuch as no net current is flowing in a path encompassed by its core 86. In this regard, any current entering the core region through one of the conductors, say Si?, is effectively cancelled out by current leaving the corey region through the other conductor 51. However, should the primary conductor 5t), 51, 52 develop a fault to ground, say within the tank 38,'the currents entering and leaving the region of the core 86` would no longer cancel out each other, and thus the winding 85 would be effectively energized. This would cause operation of the relay 9i), which, in turn, would trip the circuit breakers A, B, and C, thus effectively isolating the fault in the desired manner. It will be apparent that for any fault to ground occurring within the tank 38, irrespective of its particular location, the winding 85 will be energized to effect tripping of the breakers A, B, and C, as is desired.

In addition to being able to detect a fault occurring from the primary conductor 51, 52, Sti, within the tank 3S, the current transformer winding 85 is able to detect any faults which might occur to ground from the conductors Sti and 51 within the porcelain column 35. Whether such faults followed a path to ground via the internal surface of the porcelain column 35 or through the gaseous insulator directly to the throat 39 of the metallic tank 33, the path would still be disposed internally of the core of the auxiliary current transformer winding 35. As a result, there would be net current flowing internally of the current transformer winding 35 and such current would energize the winding 8S causing `it to produce operation of the relay 96D and resultant opening of the breakers A, B, and C, all as desired.

To insure that substantially all faults to ground occurring internally to the current transformer assembly follow a path disposed internally of the third current transformer winding 35, the tank 42 is connected to ground only at points beneath the current transformer winding 85. Thus, there is no significant likelihood of internal fault currents bypassing the third current transformer winding 35.

Any fault that might occur to ground externally to the insulating column 3S from the structure 55a or 56h at the top of the primary winding of the main current transformer, I prefer to relay as an external fault in the zone of the differential circuit 8d. To this end, a shield 93 is provided encompassing the auxiliary current transformer winding 85 and electrically interposed between the grounded components of the circuit breaker assembly (including the winding 3S) and substantially all the high voltage parts of the assembly that are susceptible to external faults. This shield 93 is connected to ground only by conductive straps 94 disposed externally to the core, or magnetic circuit, of the current transformer winding 85. As a result of this construction, external faults along the insulating column 35 are prevented from following a breakdown path to ground disposed internally of the magnetic circuit of the current transformer winding 83. Substantially all external faults in the region of the current transformer winding 35 will be to shield 93 rather than to the winding S or to the conductive parts 39, tti disposed internally of the winding, and such faults will be directed to ground through the conductive straps 94 disposed externally to the current transformer winding S5 and its core S6, thus effectively bypassing the winding 35 and the core S6. As a result, only the one differential circuit 80 in whose operating zone the external fault occurs operates its relay (70) in response to such fault. Since the interrupting ability of the breaker A would normally not be impaired by such an external fault, it would ordinarily still be capable of isolating the fault from the circuit 2d@ at the other side of the breaker A, thereby allowing uninterrupted service to be maintained over such circuit at the other side of the breaker.

It is important to minimize the possibility of a fault occurring from the lengths of conductor 53a and SSb because the protective system cannot correctly interpret the location of such a fault. For example, referring to FIG. 5, a fault from 53a or 53h to ground would appear to the protective system to be a fault in the zone of differential circuit 82. The protective system would thus open breaker A and C. This, however, would not isolate the fault from the remainder of the system since the fault is actually located between breakers A and B.

The presence of tubular conductors 56a and 56h about the conductors 58a and 58h, respectively, minimizes the chances for fault occurring from 33a or 58h. This is the case because the outside tubular conductor 56a or Sb is at substantially the same potential as the inside conductor 58a or 53h and thus acts to shield the inside conductor from the possibility of a fault to ground. Any fault occurring from the structure 56a, 58a to ground will be from the outside part 56a to ground rather than from the inside part. Similarly, any fault occurring from the struc ture Sb, 53h to ground will be from the outside part 56h to ground rather than from the inside part. It will be noted that the outside parts 56a and 56h are located in the zone of differential circuit 80, and the differential circuit will respond to such a fault to effect opening of breakers A and B, which are the correct circuit breakers to be operated for isolating the faults.

it should be understood that my invention in its broader aspects is applicable to types of circuit breakers other than those in which the high potential housing surrounds the contacts, as is the case with the tank 12 of FIG. l. For example, in the circuit breaker schematically shown in FIG. 6, there is a metallic housing 312 at high poten tial that surrounds only the operating mechanism 322 for the two pairs of contacts 316 and 318. But the contacts themselves are located in tubular porcelain housings 330 and 332 at opposite sides of the centrally located metallic housing 312. A circuit breaker of this general type is disclosed in U.S. Patent 2,997,564, Baker.

In the circuit breaker of FIG. 6, the pair of contacts 316 comprises a stationary contact 316a and a movable contact 3ll6b. The stationary contact 316g is supported from the top of porcelain housing 33t) by means of a conductive rod 326 that connects the stationary contact to a branch 11a of the power line 11. This branch 11a corresponds to the branch 11a of FIG. 3. The movable contact 31611 is arranged to be actuated by the operating mechanism 322 and is electrically connected at 3:20a to the metallic housing 312.

The pair of contacts 31S comprises a stationary contact 318g and a movable Contact 31817. The stationary contact 31851 is supported from the top of porcelain housing 332 by means of a conductive rod 328 that electrically connects the stationary contact 318:2 to a branch 11b of the power line 11. This branch 11b corresponds to the branch 11b of FIG. 3. The movable contact 318b is arranged to be actuated by the operating mechanism 322 and is electrically connected at 320I to the metallic housing 312.

The metallic housing 312 is supported on an insulating column 314 that electrically isolates the housing 312 from ground. The housing 312 will normally be at line potential by virtue of the connections 320:1 and 320b.

As pointed out hereinabove, the conductors 11a and 11b are the parallel connected branches of a power line 11. Current entering the circuit breaker of FIG. 6 through branches 11a and 11b will leave through a power line 240 electrically connected to the housing 312. The electrical circuit between 11a and 240 is constituted by parts 326, 316a, 316th, 32h61, and 312. The electrical circuit between 11b and 240 is constituted by parts 328, 318a, 318b, 32011, and 312. Thus, the two pairs of contacts 316 and 318 are electrically connected in parallel with each other; the centrally located housing constitutes one terminal of the interrupting head, and the outer end of conductor 326 lalndd32d constitute the other terminals of the interrupting While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the invention in its broader aspects. I therefore intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric circuit breaker comprising:

(a) a metallic tank at high potential,

(b) insulating means for supporting -said tank and electrically isolating said tank from ground, (c) a rst and a second pair of separable interrupting contacts disposed within said tank,

(d) a pair of spaced apart conductors projecting into said tank,

(e) means for insulating said conductors from said tank when said contacts are open,

(f) means for electrically 'connecting one contact of each of said pairs -to said tank,

(g) means for electrically connecting the other contact of said first contact pair to the inner end of a first one of said conductors so that said iirst pair of contacts and said first conductor are connected in series between said tank and the outer end of said first conductor,

(h) means for electrically connecting the other contact of said second pair to the inner end of the second of said conductors so Ithat said second pair of contacts and said second conductor are connected in series between said tank and the outer end of said second conductor,

() and means Ifor electrically connecting the series combination of said first conductor and said first pair of contacts in parallel with the series combina- -tion of said second conductor and said second pair of contacts.

2. Electric circuit breaker comprising:

(A) two interrupting heads, each comprising:

(a) a metallic tank at high potential,

(b) a first and a second pair of separable interrupting contacts disposed Within said tank,

(c) a pair of spaced apart conductors projecting into said tank,

(d) means for insulating said conductors from said tank when said contacts are open,

(e) means `for electrically connecting one contact of each of said pairs to said tank,

(f) means for electrically connecting the other contact of said first contact pair to the inner end of a irst one of said conductors so that said first pair of contacts and said first conductor are connected in series `between said' tank and the outer end of said first conductor,

(g) and means for electrically connecting the other contact of said second pair to the inner end of the second of said conductors so that said second pair of contacts and said second conductor are connected in series between said tank and the outer end of said second conductor,

(B) means for electrically connecting the series combination of said first conductor and said first pair of contacts inl parallel with the series combination of said second conductor and said second pair of contacts,

(C) insulating means for supporting said tanks and electrically isolating said tanks from ground,

(D) and means for electrically connecting the parallel circuits extending through one of said interrupting heads in series with the parallel circuits extending through the other of said interrupting heads.

3. The circuit breaker of claim 2 in which one of said interrupting heads is mounted on the other interrupting head and is electrically connected thereto even when said pairs of contacts are open.

4. The electrical circuit breaker of claim 2 in which the means for connecting the parallel circuits in series with each other comprises means for selectrically connecting the tank of one of said interrupting heads to the tank of the other of said interrupting heads.

5. An electric circuit breaker comprising:

(A) three interrupting heads, each comprising:

(a) a metallic tank at high potential,

(b) a first and a second pair of separable interrupting contacts disposed Within said tank,

(c) a pair of spaced apart conductors projecting into said tank,

(d) means `for insulating said conductors from said tank when said contacts are open,

(e) means for electrically connecting one contact of each of said pairs to said tank,

(f) means for electrically connecting the other contact of said first contact pair to the inner end of a iirst one of said conductors so that said iirst pair of contacts and said first conductor are connected in series between said tank and the outer end of said first conductor,

(g) means for electrically connecting the other contact of said second pair to the inner end of the second of said conductors so that said second pair of contacts and said second conductor are connected in series between said tank and the outer end of said second conductor,

(B) means for electrically connecting the series combination of said first conductor and said rst pair of contacts in pairallel with the series combination of said second conductor and said second pair of contacts,

(C) insulating means for supporting said tanks and electrically isolating said tanks from ground,

(D) and means for electrically connecting the parallel circuits extending through each of said interrupting heads in series with the parallel circuits extending through the other interrupting heads,

(E) said connecting means between said heads comprising an electrical connection between the tanks of two of said heads that is present even when said contacts are open.

6. The circuit breaker of claim 5 in which one of the tanks that is electrically connected to another tank is mounted on said other tank.

7. The electric circuit breaker of claim l in combination with:

(a) a current transformer assembly comprising an insulating enclosure, a pair of current transformer terminals, and a primary circuit extending between said terminals internally of said enclosure,

(b) two lengths of conductor, one of which extends between one of said current transformer terminals and the outer end of one of the conductors projecting into said tank and the other of which extends between said one current transformer terminal and the other end of the other conductor projecting into said tank,

(c) a pair of tubular conductors respectively surrounding said lengths of conductor,

(d) means for connecting said tubular conductors to the other of said current transformer terminals at one end of each tubular conductor and for connecting said tubular conductors to a power line at points spaced from said one end,

(e) sole electrical connection between each of said lengths of conductor and its respective tubular conductor being through said primary circuit.

8. The electric circuit breaker of claim 1 in combination with:

(a) a current transformer assembly comprising an insulating enclosure that serves as the insulating means for supporting said tank, a pair of current transformer terminals, and a primary circuit extending between said terminals internally of said enclosure,

(b) and means for forcing all current flowing through the two parallel paths extending through said circuit breaker to fiow through said primary circuit comprising means for connecting the outer end of both of said conductors to one of said current transformer terminals.

9. An electric circuit breaker comprising:

(a) a metallic housing at high potential,

(b) insulating means for supporting said housing and electrically isolating said housing from ground,

(c) a first and a second pair of separable interrupting contacts,

(d) a pair of spaced apart conductors for respectively carrying current to said pairs of contacts,

(e) means for insulating said conductors from said housing when said contacts are open,

(f) means for electrically connecting each of said pairs to said housing,

(g) means for electrically connecting the other contact of said first contact pair to the inner end of a first one of said conductors so that said first pair of contacts and said first conductor are connected in series between said housing and the outer end of said first conductor,

(h) means for electrically connecting the other contact of said second pair to the inner end of the second of said conductors so that said second pair of contacts and said second conductor are connected in series between said housing and the outer end of said second conductor,

(i) and means for electrically connecting the series combination of said first conductor and said first pair of contacts in parallel with the series combination of said second conductor and said second pair of contacts.

10. Electric circuit breaker comprising:

(A) two interrupting heads, each comprising:

(a) a metallic housing at high potential,

(b) a first and a second pair of separable interrupting contacts,

(c) a pair of spaced apart conductors for respectively carrying current to said pairs of contacts,

(d) means for insulating said conductors from said housing when said contacts are open,

(e) means for electrically connecting one Contact of each of said pairs to said housing,

(f) means for electrically connecting the other contact of said first contact pair to the inner end of a first one of said conductors so that said first pair of contacts and said first conductor are connected in series between said housing and the outer end of said first conductor,

(g) and means for electrically connecting the A other contact of said second pair to the inner end of the second of said conductors so that said second pair of contacts and said second conductor are connected in series between said housing and the outer end of said second conductor,

(B) and means for electrically connecting the series combination of said first conductor and said first pair of contacts in parallel with the series combination of said second conductor and said second pair of contacts,

(C) insulating means for supporting said housing and electrically isolating said housing from ground,

(D) and means for electrically connecting the parallel circuits extending through one of said interrupting heads in series with the parallel circuits extending through the other of said interrupting heads.

one contact of 11. The circuit breaker of claim 1() in which one of said interrupting heads is mounted on the other interrupting head and is electrically connected thereto even when said pairs of contacts are open.

12. The electric circuit breaker of claim 10 in which the means for connecting the parallel circuits in series with each other comprises means for electrically connecting the housing of one of said interrupting heads to the housing of the other of said interrupting heads.

13. An electric circuit breaker comprising:

(A) three interrupting heads, each comprising:

(a) a metallic housing at high potential,

(b) a first and a second pair of separable interrupting contacts,

(c) a pair of spaced apart conductors for respectively carrying current to said first and second pairs of contacts,

(d) means for insulating said conductors from said housing when said contacts are open,

(e) means for electrically connecting one contact of each of said pairs to said housing,

(f) means for electrically connecting the other contact of said first contact pair to the inner end of a first one of said conductors so that said first pair of contacts and said first conductor are connected in series between said housing and the outer end of said first conductor,

(g) means for electrically connecting the other contact of said second pair to the inner end of the second of said conductors so that said second pair of contacts and said second conductor are connected in series between said housing and the outer end of said second conductor,

(B) means for electrically connecting the series combination of said first conductor and said first pair of contacts in parallel with the series combination of said second conductor and said second pair of contacts,

(C) insulating means for supporting said housing and electrically isolating said housings from ground,

(D) and means for electrically connecting the parallel circuits extending through each of said interrupting heads in series with the parallel circuits eX- tending through the other interrupting heads,

(E) said connecting means between said heads comprising an electrical connection between the housing of two of said heads that is present even when said contacts are open.

14. The circuit breaker of claim 13 in which one of the housings that is electrically connected to another housing is mounted on said other housing.

References Cited in the file of this patent UNITED STATES PATENTS 2,804,576 Goggeshall et al. Aug. 27, 1957 2,931,951 Wilson Apr. 5, 1960 3,032,689 Baker et al. May 1, 1962 

1. AN ELECTRIC CIRCUIT BREAKER COMPRISING: (A) A METALLIC TANK AT HIGH POTENTIAL, (B) INSULATING MEANS FOR SUPPORTING SAID TANK AND ELECTRICALLY ISOLATING SAID TANK FROM GROUND, (C) A FIRST AND A SECOND PAIR OF SEPARABLE INTERRUPTING CONTACTS DISPOSED WITHIN SAID TANK, (D) A PAIR OF A SPACED APART CONDUCTORS PROJECTING INTO SAID TANK, (E) MEANS FOR INSULATING SAID CONDUCTORS FROM SAID TANK WHEN SAID CONTACTS ARE OPEN, (F) MEANS FOR ELECTRICALLY CONNECTING ONE CONTACT OF EACH OF SAID PAIRS TO SAID TANK, (G) MEANS FOR ELECTRICALLY CONNECTING THE OTHER CONTACT OF SAID FIRST CONTACT PAIR TO THE INNER END OF A FIRST ONE OF SAID CONDUCTORS SO THAT SAID FIRST PAIR OF CONTACTS AND SAID FIRST CONDUCTOR ARE CONNECTED IN SERIES BETWEEN SAID TANK AND THE OUTER END OF SAID FIRST CONDUCTOR, 